In the previous funding period, we used eNOS and iNOS knockout mice to demonstrate that physiologic production of nitric oxide (NO) by endothelial nitric oxide synthase (eNOS) suppresses atherosclerosis, whereas pathologic production of NO by inducible NOS (iNOS) contributes to atherosclerosis. We found that eNOS knockout mice demonstrate an exaggerated response of neointimal proliferation in response to vessel injury. Furthermore, when fed a Western type diet, eNOS/apoE dko mice develop more severe atherosclerosis than do apoE knockout mice, as well as complications of aortic aneurysms, aortic dissection, distal coronary artery disease, myocardial infarction, and ventricular dysfunction. In contrast, iNOS/apoE dko mice develop less atherosclerosis, and show evidence for decreased levels of lipid oxidation. We propose now to extend these results by examining the molecular and cellular mechanisms by which abnormalities in eNOS expression contribute to atherosclerosis. Specifically, we hypothesize that abnormalities in eNOS phosphorylation at serine 1179 and threonine 497 underlie the molecular mechanisms of endothelial dysfunction, and that statins and estrogens exert their beneficial effects by correcting these abnormalities. We are generating transgenic and knockin mice that carry mutations at these phosphorylation sites, to mimic both the phosphorylated form (aspartate substitution) and an unphosphorylatable form (alanine substitution). These mice will be useful tools to determine the extent to which abnormalities in phosphorylation lead to increased vessel injury response, and propensity to diet induced atherosclerosis in the apoE knockout mouse model. A second hypothesis is that expression of NOS isoforms by circulating cells, in addition to vascular endothelium and smooth muscle, affects atherosclerosis. We propose to use bone marrow transplantation studies to assess the importance of NOS isoform expression by bone marrow-derived cells to vessel injury and atherosclerosis in vivo.